Many advances have been made recently toward reducing the emissions and increasing the efficiency of Diesel engines. One such advancement has been the development of Homogeneous Charge Compression Ignition (HCCI) systems. HCCI is a process wherein an initial premixed, homogeneous charge of Diesel fuel and air is compressed and partially burned by high temperature and pressure in a flameless process, followed by one or more post injections of fuel, as opposed to classic Diesel ignition wherein a charge of air is compressed and then injected with Diesel fuel, resulting a stratified mixture of fuel and air. HCCI has yielded many benefits including extremely low emissions of NOx and particulate matter (soot) because of lower ignition temperatures and the use of a leaner fuel/air mixture.
However, HCCI has its challenges. For example, with a compression ratio in the range of 9:1 to 14:1, starting an HCCI-ignited engine in cold weather can be difficult. This challenge can be addressed by selectively varying the point at which the intake valves close during the engine cycle to controllably reduce the compression ratio from that of a higher designed value, optimized for cruising conditions. By selectively keeping the intake valve open for a portion of the compression stroke, a portion of the volume of air that would otherwise be compressed in the cylinder by the up-moving piston, is instead bled back through the open intake valve, thereby effectively reducing the compression ratio on the engine.
Mechanization of an HCCI strategy that can selectively vary the compression ratio has been proposed in the past with limited success because of system and hardware complexity. For example, mechanization has been achieved by using two separate cam phasers to operate two intake valves at each cylinder so that intake valve opening and intake valve closing can be controlled by the phasers independently. Although effective, the use of two cam phasers is costly, adds weight to an engine and vehicle and often cannot be fitted into available space.
What is needed in the art is a simplified mechanism for selectively varying the closing point of the intake valves of an HCCI engine that is relatively easy to manufacture and assemble, has few parts, and requires minimal packaging space in an engine envelope.
It is a principal object of the present invention to provide variable closing timing of intake valves of an internal combustion engine.
It is a further object of the invention to simplify the manufacture and assembly of a system for such variable closing timing.